I've designed interfaces for desktop applications and Web. I am new to JDE and Blackberry development, but one thing my group keeps in mind when designing interfaces is the level of knowledge the user(s) may have. If they are a saavy user, then your interfaces could probably include more complexity. If they are total newbies, then simplicity is the rule of thumb.
A great book on usability is Tognazzi on Interface Design. Regardless of the platform you work, the principals found in the book is what has help shaped useful and engaging interfaces.
I am working on a form as well
I just cracked open my first venture and am getting the hang of it I think.